Endoscopy is an important, non-destructive inspection method for examining, in medicine and technology, small cavities which in general are difficult to access. In an endoscope, a distal end is distinguished from a proximal end. The distal end refers to the “remote” end of an endoscope which is introduced into an object for observing internal structures, while the proximal end basically remains outside the examined cavity. In this process, viewing the image is made through the proximal end, e.g. by means of a look into an ocular or by connecting a camera. While in the past the endoscopic inspection has been performed manually by the human examiner or doctor, is has been tried in recent time, in the course of the development of automatic visual examination systems, to increasingly deploy automated endoscopic examination systems.
Especially in the area of hydraulic or pneumatic devices (e.g. brake cylinders, control elements etc.) with functional bore surfaces, there are high quality demands often necessitating full control of the entire production. This examination offers a high rationalization potential if corresponding endoscopic examination automatics are available.
Substantially, two basic approaches for illuminating cavities during an endoscopic examination thereof are known.
On the one hand, miniature lamps attached to the distal end of the endoscope, for example, serve for illuminating the sensed scene or environment. The relatively large design, even of miniature lamps, which makes the deployment in very small, thin endoscopes impossible, is one disadvantage. The relatively high portion of thermal emission is also problematical in this technique. In lamps with a higher power, this quickly leads to an inacceptably high heat input into the object examined.
For this reason, the technique predominantly used nowadays is a fiber-optically input cold light illumination. In this context, an efficient light source (e.g. a halogen lamp or an arc lamp) is located outside the cavity. The light output is gathered by means of optics (mirrors, condensers) and transferred to the tip of the endoscope by fiber optic light guides, and there, it exits at the end of the light guide fibers. Minimizing the transferred infrared portion is achieved by suitable infrared blocking filters. The light such filtered is also referred to as “cold light”. The disadvantages of this technique are the illumination arrangement constructively fixedly predetermined by the light exit at the fiber bundle, the lossy light transmission as well as the efficient, expensive cold light sources necessitated.
In recent time, the external cold light sources have also been replaced by external LED light sources with high-efficiency LEDs (LED=light-emitting diode or a light-generating semiconductor element).
In most of the endoscopes available on the market, the integrated fiber optic illumination is implemented in a dark field arrangement. Due to the avoidance of shiny and dazzling effects, this kind of illumination has proved to be especially suitable for the human viewer.
In the dark field arrangement, a light-guiding fiber bundle is attached to the shaft of the endoscope, so that the light exit is close to or coaxially around the distal objective. In this context, the light exit at the fiber bundle is fixedly predetermined by the construction of the device, so that apart from the total intensity of the illumination, no further illumination parameters may be influenced by regulation of the external light source.
In the automatic technical endoscopy, the inspection of a cavity (a bore) is made without human intervention by an image processing system motor-driving an endoscope with a video camera and an accordingly suitable illumination into and out of the cavity for an automatic image gain. The images thus gained are automatically evaluated by means of image processing algorithms. Thus, an evaluation of the cavity (or device) examined is determined, which in turn may be used for sorting out defective parts.
In many devices, the dark field illumination commonly integrated by endoscope manufacturers has proved to be not quite suitable and a part field illumination has proved to be advantageous for the automated examination by means of image processing algorithms. Using the bright field illumination, several arrangements are known in the endoscopic bore examination. For through bores with two openings, the introduction of the endoscope is made from one side of the bore, and the introduction of the illumination, e.g. in the form of a light finger, is made from the other side. A light finger is a rod or “finger”-shaped rigid or flexible apparatus at the end of which light exits by means of a fiber optic light guide, for example. The image sensing is made by a simultaneous movement of the endoscope and the illumination through the bore with a constant distance, so that a constant bright field arrangement is guaranteed during the entire image capture, considering the bore diameter, the image angle of the optics etc.
This is not possible with sack bores having only one opening. Here, the light source may be mounted to a carrier in front of the distal endoscope tip and be introduced with the endoscope into the bore. In this process, the illumination is broadly emitting and directed to the optics, so that in turn a bright field illumination is achieved, considering the geometrical frame conditions. Another approach works with an “all-round backward look”. In this context, the visual field is circumferentially turned over 360 degree to the side or backwards via a suitable mirror in front of the endoscope or a so-called Greguss lens. By an illumination attached around the shaft of the endoscope in a slightly offset manner, a bright field arrangement may in turn be achieved. Both approaches have in common the disadvantage that the base, or the last portion of the bore wall of the sack bore, cannot be sensed.
With respect to the endoscope illuminations deployed up to date, it should be noted, however, that the endoscopes nowadays available on the market substantially without any exception comprise illumination apparatuses whose mode of operation is optimized for viewing the endoscopic image by humans. Since in automated, endoscopic examination systems the images gained are not anymore sensed by the eye and are not anymore evaluated by humans, but are sensed and evaluated by cameras and image-processing pattern recognition algorithms in computers, other, new endoscope illuminations are needed to gain high-quality images for machine sensing (machine viewing). Thus, there is a particular need for illumination apparatuses for endoscopes which allow an optimized image gain in visual examination automates. Thereby, it should become possible to economically solve a large number of difficult examination tasks in devices with internal surfaces by means of automatic endoscopic visual examination systems, which up to date have not been feasible or have only been feasible with high personnel expenses and the associated costs.